1. Open Active Directory Users and Computers.
2. If not already select, enable Advanced Features by clicking View | Advanced Features.
3. Expand the nodes until you have located the user of concern.
4. Right-click the user and select Properties.
5. Switch to the Exchange Advanced tab and click the Protocol Settings button.
6. From the Protocols page, click HTTP.
7. From the HTTP Protocols Detail page, deselect the Enable for mailbox setting.
8. Close out all properties pages and the Active Directory Users and Computers console.